Sorbent cartridges operate by adsorbing ions and other waste solutes from a fluid, such as dialysate. In addition to removing wastes, such as urea, phosphates and non-polar molecules, sorbent cartridges can also remove non-waste ions from the dialysate, such as potassium, calcium and magnesium. Certain common sorbent materials, such as zirconium oxide and zirconium phosphate are expensive. Removal of both wastes and non-waste components from dialysate results in a need for a large amount of these expensive sorbent materials, raising the costs of sorbent dialysis.
To avoid the use of sorbent based regeneration, some systems recirculate dialysate back to a patient multiple times. One such dialysis system is described in U.S. Pat. No. 8,034,017. The known system is intended for at-home, nocturnal use, and includes a dialyzer and two containers along with pumps to regulate flow into the dialyzer. The system operates by circulating dialysate from the containers to the dialyzer and back into the containers. The system has no sorbent cartridge system to remove contaminants in the dialysate, and instead relies on a large starting volume of 10-20 L to provide sufficient buffering and dilution capacity throughout a therapy session. However, the level of contaminants introduced from the spent dialysis can be significant enough to affect therapy. Although a dialysate flow rate can be reduced to use a smaller volume of dialysate, a lower flow rate also reduces the flux rate of contaminants across the dialyzer membrane, thereby increasing the necessary dialysis time. Further, the system cannot add substances or regulate electrolyte or pH levels during operation.
Although the cost of water is generally less than the cost of sorbent materials, dialysis systems that reuse spent dialysate require a relatively large amount of clean source water to use in generating the dialysate. In many parts of the world, large amounts of pure water are not readily available. In contrast, use of a sorbent cartridge in order to remove wastes from dialysate during dialysis can allow for a dialysis session with significantly less clean water. Because the patient's wastes are removed from the dialysate, the dialysate can be recirculated back to the dialyzer without the need for disposal. Use of a sorbent cartridge also reduces the amount of source water to which the patient is exposed. Source water may contain certain contaminants, and exposing the patient to less source water can reduce the amount of these contaminants to which the patient is exposed.
As such, a system is needed to eliminate the problems associated with reusing spent dialysate without full regeneration of the spent dialysate in a cost-effective manner. There is a need for a system that can provide a dual system of passing dialysis multiple times through a dialyzer that cooperates with a sorbent based regeneration system to selectively regenerate dialysate at a desired time or condition. The system should be able to regenerate dialysate selectively, intermittently, and on-demand. The systems should allow for the use a smaller amount of sorbent material and a shorter dialysis time than described in known prior art, such as the standard 2-4 hour dialysis sessions. There is also a need for a system that can reduce the amount of sorbent materials necessary for carrying out sorbent dialysis without increasing the amount of clean water required. There is further a need for systems and methods that allow for regeneration of dialysate less often during a dialysis session, thereby lowering the sorbent material requirements while maintaining effective treatment of dialysis patients.